In general, speakers used in the field of pure-audio and the like are demanded to yield full and rich tone, while ensuring sufficient volume.
Conventional speakers which have been proposed include cone speakers wherein a diaphragm is formed in a conical shape, so-called dome speakers wherein a diaphragm is formed in a half-sphere shape and the convex side thereof is used as the sound generating portion, and so forth (see Electric & Electronic Engineering Encyclopedia Vol. 25 “Audio Video”, supervising editor Shigeo Tsuji, Published November 1983 from Denkishoin, and also Japanese Unexamined Patent Application Publication No. 11-196485).
With a conventional cone speaker, a cone-shaped diaphragm generates sound waves by back-and-forth piston movement, so a great volume can be readily obtained, but the diaphragm simply performs piston motions back and forth, so the emission wavefront of the sound wave is generally a planar wave. That is to say, this is not a spherical wave as with dome speakers mentioned above, so air disturbance (vortex) occurs due to a difference in air pressure at the boundary between a vibration region and a non-vibration region, disturbing sound waves and rendering it difficult to obtain a full and rich tone. The vibration region as used herein means a generally pillar-shaped region of which the base face is the diaphragm, and the air is directly vibrated by vibrations of the diaphragm.
On the other hand, the latter dome speaker generates sound waves by breathing actions wherein the diaphragm stretches and shrinks, so the sound waves are naturally spherical waves. Such spherical waves are advantageous in yielding full and rich tone as described above, without air disturbance (vortex).
However, such dome speakers have a structure wherein only the perimeter portion of the half-sphere diaphragm is securely held, rather than a structure such as with the cone speaker wherein the entire diaphragm moves, and moreover, sound waves are generated by breathing actions, so great amplitude cannot be expected. Accordingly, great volume, and base sounds which require great vibrations, are difficult to obtain.
Non-Patent Document 1: Electric & Electronic Engineering Encyclopedia Vol. 25 “Audio Video”, supervising editor Shigeo Tsuji, Published November 1983 from Denkishoin
Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-196485